It is generally known that an exhaust gas of an internal combustion engine such as a diesel engine contains harmful substances such as NOx, SOx and smoke and dust or substances that apply load to the environment. Thus, various schemes have been proposed for reducing such substances.
Conventionally, a method for controlling an air excess ratio to an appropriate value is known as one method for reducing smoke, dust and/or the like.
For example, PTL 1 (below) discloses a method for estimating a flowing state of an in-cylinder gas of an internal combustion engine, taking into account the estimated flowing state of the in-cylinder gas to estimate a value equivalent to a concentration of an air-fuel mixture of fuel and intake air as an air-fuel mixture concentration equivalent value, and adjusting engine control parameters (e.g., fuel injection timing, fuel injection pressure, amount of fuel injection, amount of exhaust gas recirculation) so that the estimated air-fuel mixture concentration equivalent value matches a predetermined concentration.
PTL 1: Japanese Unexamined Patent Application, Publication No. 2005-226460